1. Field of the Invention
The present invention relates to a lateral IGBT (Insulated Gate Bipolar Transistor), and more particularly to a lateral IGBT employing an SOI (Semiconductor On Insulator) substrate.
2. Description of the Related Art
An IGBT is one of power semiconductor devices of the insulated gate type. The IGBT is a new power semiconductor device having both a high speed switching property of a power MOSFET and a high output property of a bipolar transistor. For this reason, in recent years, IGBTs are frequently used in the field of power electronics, such as an inverter, a switching power supply, or the like. Among the IGBTs, a lateral IGBT draws attention, since it is suitable for a high degree of integration level. In general, the lateral IGBT is formed, using an SOI substrate.
Where a large current is treated in power devices, such as an IGBT, the current capacity of a power output stage is important. A power stage having a current capacity of 1A has been developed as a power stage of 500 V class. However, in order to treat a large current, a surface area of the power stage has to be formed larger in proportion to an increase of the necessary current capacity. For example, where 5A is treated, the surface area of the power stage becomes five times larger, thereby making a chip bulky. Therefore, it is necessary to increase a current density per unit area and to keep a chip size compact so as to avoid the above described problem.
However, there is a problem in IGBTs, especially in a lateral IGBT, such that electron injection is not sufficient and thus its current density is hardly increased.
As described above, since an IGBT, which is one of the power devices, has both a high speed switching property and a high output property, it is employed in the field of power electronics. However, on the other hand, the IGBT has a problem such that its current density is hardly increased.